Preparing the greenhouse for ornamentals

by Sally Colby
Sinclair Adam says ornamental growers should take time both now and as the season progresses to take steps to ensure that everything is in place for the upcoming growing season.
Adam, an extension educator in Pennsylvania, helps growers understand the importance of good sanitation between crops. “Many growers go through the house and sanitize to control biological contaminants that occur naturally,” he said. “Many buildings have roll-up sides, and whatever is in the atmosphere can accumulate on the surfaces on the greenhouse. All of those surfaces should be cleaned.”
In his work with the Penn State Trial Gardens, Adam says part of the protocol includes maintaining a high degree of security. “We’ll physically clean everything,” he said. “We use a broom on the floors and wash the plastic sides and ceilings, then go back in with Green-Shield® and scrub down all the bench surfaces. We’ll use a sprayer to clean the floor to get as many biological contaminants out of the loop as possible.”
The timing of cleaning is important, and Adam says growers should do such cleaning as close as possible to the time plants are started or arriving from another source. “If first entry to the building is February, we clean in December/January,” he said. “The closer to start-up, the better. We want everything as clean as possible — no botrytis, no contaminants, no weeds. That’s one of the most significant things the grower can do to ensure good crop quality.”
Pots and trays that are kept over from one year to the next should be thoroughly sanitized. “When we plant into the five-gallon pots that will go to the field, those pots are washed with a high-pressure wash including Green-Shield®,” said Adam. “We reuse them until they’re beyond repair.”
Adam reminds growers that it’s important to remove soil from pots and tools prior to sterilizing so that the active ingredients in products can work most effectively. If bagged soil is held over from prior growing year and bags are still sealed, that soil can be used the following season. If the bag is open, it might be difficult to ensure clean, sterile media.
Adam says it’s important for growers to understand the biology of the crop they’re growing and what that crop is most susceptible to in order to prepare the most ideal growing conditions. For example, the bacterial disease Xanthomonas that occurs on geraniums and begonias comes from two different races. Some diseases, such as impatiens necrotic spot virus (INSP), cannot survive outside the host plant.
Petunias are especially sensitive to viruses, and many viruses are transmitted by insects.
The exception is tobacco mosaic virus (TMV) which is transmitted by people. Greenhouse managers should make sure employees are washing effectively and are aware of how TMV is spread. “If you’ve handled tobacco products such as smoking a cigarette or putting chewing tobacco in your mouth, you’ve touched the tobacco,” said Adam. “You can spread tobacco mosaic virus if the tobacco product you handled had the virus. It’s important that greenhouse operations have strict protocols about how people are to proceed after lunch or a break. If they put their hand in their pocket after smoking a cigarette, their pocket can become contaminated with the virus. If they touch the doorknob to go back into the building, the doorknob can be contaminated and the next person, perhaps not a tobacco user, touches the doorknob is now a vector for the spread of disease.”
Adam explains mishandling and wounding of plant tissue during handling and then placing those plants in flats that have not been properly sanitized can result in an outbreak of pythium. “Some operations won’t recycle plastic, but that leads to plastic waste problems,” he said. “If you are going to reuse trays, pots and flats, make sure they’re clean and store them carefully so they’re not contaminated while they’re in storage.”
Banging trays or pots against a trash can isn’t sufficient to remove residual organic material — if items aren’t clean or if they are cracked, they can’t be adequately sanitized.
“It’s best to get the residue off before immersing the pot or flat,” said Adam. “A scrub brush is a wonderful thing. Annual trays aren’t that expensive, but some of the perennials, especially if they’re patented, can be over $100/flat wholesale. It takes a couple of minutes to clean that with a brush, so it doesn’t even cost one dollar to clean the tray but the product going back into it is worth more than $100 so it’s a no-brainer on the accounting side.”
One issue that many growers have dealt with lately is downy mildew issues with basil and other crops. “Downy mildew is a persistent organism in nature, and can survive three to five years in soil,” said Adam. “There are also significant problems with Pythium or root rot. We don’t see to much of that when the soil is warm or hot, so it isn’t a big deal in June, July and August. But in the cold, dark months, it is a problem.”
The down time between crops is a good time to check the irrigation system and irrigation water. “If it’s surface water coming from a pond or retention basin, it should be sampled periodically,” said Adam. “If you draw the level down significantly during the active growing season and you’re into the lower depths, the contaminant level might be higher. It’s important to test the water because of chemistry. If you have hard water or if it has a pH that’s too high or low, that can affect pesticide use and viability.” Adam says pH can be influenced by the level of rainfall, so off-season water testing is important. “Rainwater is getting into groundwater, and if that isn’t being recharged at a constant rate, the pH will change,” he said. “The parent rock material that surrounds the well contributes to irrigation pH.” Adam noted calcium is often noted as a factor that influences pH, but magnesium and other elements also influence pH.
Adam noted that watering is an important task in the greenhouse, and that workers should be well-trained in proper watering techniques during the off-season and throughout the year to ward off problems before they start. “Many root zone problems are brought on by poor watering practices, so you want the best person on watering,” he said. “It’s also good to train assistants and those who will be doing weekend watering.”
Growers should become familiar with the diseases are most likely to affect the crops they grow, and to know the symptoms that help identify those diseases. “If you’re growing bedding plants, you know what to expect,” said Adam. “Be able to identify the symptoms and signs of disease is something you can do without a microscope. Every grower should build those skills to have fewer losses.”